Device for depositing sheets on a stack

ABSTRACT

Apparatus for depositing sheets on a stack, which permits essentially free access to the stack and can be implemented with a low outlay of materials and costs. The apparatus includes on the side of the stack ( 1 ) that faces a machine, tongues ( 5, 6 ) with which frictional elements ( 3, 4 ) can be brought into and out of contact and which can be moved in the conveying direction ( 10 ) of the sheets ( 2 ) and in the opposite direction, and can be lowered onto the stack ( 1 ), and wherein on the side of the stack ( 1 ) that faces the machine, at least one hold-down ( 7 ) is provided which can be moved in the conveying direction ( 10 ) of the sheets ( 2 ) and in the opposite direction, and can be lowered onto the stack ( 1 ).

FIELD OF THE INVENTION

The invention relates to an apparatus for depositing sheets on a stack.

BACKGROUND OF THE INVENTION

Apparatus is known for depositing sheets on a stack, which apparatus isarranged downstream, for example, of a printing machine. Such apparatususes grippers that are arranged on endless chains, open under camcontrol and allow a sheet to fall in order to form a stack. Allowing thesheet to fall can be improved by using suction air and blower devices,by the conveying speed being retarded considerably and by the fallingmovement being accelerated. In order to improve the exactness of thestack formation, the sheets to be deposited are brought up against astop and aligned using rectilinear joggers acting on side edges. In theenvironment of the stack there is a large number of constructionalelements requiring high outlay of materials and costs, which also impairoperator accessibility to the stack for handling and inspectionactivities. The moving parts in the sheet stack area of a printingmachine constitute a safety risk, so that the sheet stack area isenclosed to the greatest possible extent. In order to remove a proofsheet, appropriate additional apparatus, such as flaps or diverters, canbe provided, which necessitates additional outlay.

SUMMARY OF THE INVENTION

The object of the invention is to develop an apparatus for depositingsheets on a stack, which permits essentially free access to the stackand can be implemented with a low outlay of materials and costs.

The elements provided for depositing the sheets are located essentiallyso as to face the sheet-processing or sheet-inspecting machine. Theelements act on the trailing end of the sheets and occupy only a lowvolume. Free accessibility to three sides of the stack is provided. Ifthe sheets are deposited with the imprint on the top, the printed imagecan be inspected easily, since only a small area is covered by suchelements and the light conditions for the inspection are optimal. Thestack can be transported away without hindrance. If the frictionalelements are independently driven rollers, a skewed position of a sheetcan be compensated for. If, in addition, the frictional elements can bemoved transversely with respect to the conveying direction of thesheets, the lateral position of the sheets can be adjusted. Theapparatus has only a few elements with a low volume. Stops or depositcontainers predefining the form of the stack are not necessary. Thewidest possible range of sheet format can be deposited, withoutadjustments of any kind being needed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is to be explained in more detail below using theexemplary embodiments. In the drawings:

FIGS. 1.1 through 1.11 show a schematic side view of the apparatus, atvarious stages of operation;

FIG. 2 shows a schematic plan view of the apparatus; and

FIGS. 3 through 7 show an embodiment with control cams.

DETAILED DESCRIPTION OF THE INVENTION

Those parts of the apparatus, which are essential to the invention areillustrated schematically in side view and plan view in FIGS. 1.1through 1.11 and 2. FIGS. 1.1 through 1.11 show a stack 1, onto whichsheets 2 are to be deposited horizontally upon one another. For thispurpose, two rollers 3, 4, two tongues 5, 6, and hold-down 7 areprovided. The axes of rotation of the rollers 3, 4 are aligned along aline 8, which is parallel to the upper, rear stack edge 9 andperpendicular to the conveying direction 10. In the lateral direction,the rollers 3, 4 are arranged symmetrically with respect to the mid-line11 of the stack 1, in the vicinity of the side edges 12, 13 of the stack1. The rollers 3, 4 are driven independently of one another by steppingmotors, so that the rollers 3, 4 can rotate at different speeds in thedirection of the arrow 16.

The rollers 3, 4, together with the stepping motors, are fixed to acommon frame 17. The frame 17 with the rollers 3, 4 is provided suchthat it can be raised and lowered in the vertical direction 18 andpositioned in the lateral direction 19. On their surface, the rollers 3,4 are provided with an elastic material, so that when they are incontact with a sheet 2, the result is a high coefficient of friction.The tongues 5, 6 are located in the lateral direction at the level ofthe rollers 3, 4. The tongues 5, 6 are very flat, arranged parallel tothe surface of the stack 1 and fixed to a frame 20. The frame 20 withthe tongues 5, 6 can be positioned in the vertical direction 18 and inthe horizontal direction 21. The surface 22 of the tongues 5, 6 facingthe rollers 3, 4 is polished and, in relation to the sheet material, hasa low coefficient of friction. The surface 23 of the tongues 5, 6 facingthe upper side of the stack can have a high coefficient of friction inrelation to the sheet 2 located underneath. The hold-down 7 acts in thecenter on the rear stack edge 9. The hold-down 7 is likewise arrangedsuch that it can be positioned in the horizontal and vertical direction18 and 21. The underside 24 of the hold-down 7 has a high coefficient offriction in relation to the sheet 2 located underneath.

The mode of action of the apparatus is to be explained using elevencomponent pictures FIGS. 1.1 through 1.11: in the initial state (FIG.1.1) the rollers 3, 4 and the tongues 5, 6 are raised, in each case, intheir uppermost vertical position. The hold-down 7 presses with itsunderside 24 on the top sheet of the stack 1 and fixes it. The rollers3, 4 rotate at a circumferential speed, which corresponds to theconveying speed of a sheet 2 output from a printing machine. Theconveying direction 10 is inclined with respect to the horizontaldirection 21 in such a way that the sheet 2, beginning with its leadingedge 25, can slide along on the smooth surface 22 of the tongues 5, 6.

In the state shown in FIG. 1.2, the tongues 5, 6 have been lowered ontothe stack 1, and the rollers 3, 4 have been lowered to about half theirmaximum height above the stack 1. As the sheet 2 is advanced further,the leading end is located under the rollers 3, 4, as illustrated inFIG. 1.3. The rollers 3, 4 press the sheet 2 against the surface 22. Thesheet 2 is conveyed onward by the rotation of the rollers 3, 4. Thestepping motors of the rollers 3, 4 are stopped when the trailing edge26 of the sheet 2 has reached the rear stack edge 9. This state is shownin FIG. 1.4.

After the rollers 3, 4 have stopped, the hold-down 7 is lifted off thestack 1 and, as illustrated specifically in FIG. 1.5, displaced in thehorizontal direction 21 in the direction opposite to the conveyingdirection 10 of the sheet 2, so that the front end 27 of the hold-down 7is still located in front of the rear stack edge 9. At the same time,the sheet 2 is deposited onto the stack 1 in the area between thetongues 5, 6. As the hold-down 7 is drawn away, the sheet 2 remainsfixed in position by the rollers 3, 4. As shown in FIGS. 1.6 and 1.7,the hold-down 7 is placed onto the rear end of the stack 1 again by ahorizontal movement and a vertical movement. The hold-down 7 then takesover the action of fixing the top sheet 2 in position.

The rollers 3, 4 can be lifted off the stack 1, as shown in FIG. 1.8. Insubsequent steps (FIGS. 1.8 and 1.9), the tongues 5, 6 are lifted offthe stack 1 and drawn back in the horizontal direction 21 to such anextent that the front end 27 of the tongues 5, 6 is still located infront of the rear stack edge 9. The sheet 2, which continues to be fixedby the hold-down 7, is deposited entirely on the stack 1. In a laststep, as illustrated in FIG. 1.11, the tongues 5, 6 are moved back intothe position above the stack 1 and under the rollers 3, 4. The rollers3, 4 are set rotating, which produces the initial state, described inFIG. 1.1, for the deposition of the next sheet 2.

The stepping motors of the rollers 3, 4 can be constituent parts of aposition control loop for the sheets. For this purpose, detectors forthe position of the sheet 2 in relation to the stack edges can beprovided. By comparing the actual position with a desired position,actuating signals can be derived which, in the step according to FIG.1.3, drive the rollers 3, 4 at different circumferential speeds in sucha way that a skewed position of a sheet is compensated for. In the stepaccording to FIG. 1.4, the frame 17 with the rollers 3, 4 can bepositioned further in the direction 19, by which any lateral offset ofthe sheet 2 in relation to the stack 1 can be compensated for or can beproduced deliberately.

FIGS. 3 through 7 show an exemplary embodiment in which two tongues 101,102 and a hold-down 103 arranged between the tongues 101, 102 can beraised and lowered from a stack (not further illustrated) with the aidof cam disks 104–106. The cam disks 104–106 are firmly seated on a shaft107, which is mounted in a frame 108. In order to drive the shaft 107, atoothed-belt gear mechanism is used, having toothed-belt pulleys109–111, a toothed belt 112, and a motor 113 fixed to the frame 108. Thetongues 101, 102 are connected via rotary joints 114, 115 to a commonholding plate 116 which is essentially arranged horizontally and whichis mounted such that it can be pivoted on a shaft 117 held in the frame108. The hold-down 103 is likewise connected via a rotary joint 118 to aholding plate 119, which is also mounted such that it can be pivoted onthe shaft 117.

Mounted in the frame 108 is a further shaft 120, which is locatedparallel to the shaft 107 and on which cam disks 121–123 are fixed. Thecam disks 121–123 roll on grooved ball bearings 124 (FIG. 5), which arelocated in the U-shaped holding plates 116, 119. As the bottom view ofFIG. 4 reveals, the cam disks 104–106 slide on sliding coverings125–127, which are located under the tongues 101, 102 and under thehold-down 103. The shaft 120 is driven synchronously with the shaft 107by the toothed-belt pulley 110. In order to prevent the tongues 101,102, the hold-down 103 and the holding plates 116, 119, all of which aremoved in operation, from lifting off the cam disks 104–106, 121–123,tension springs 128–130 are provided, which are fixed to a shaft 131fixed in the frame 108. On the shaft 117, close to the holding plate119, a tension holding plate 132 is mounted such that it can be pivoted.Provided in the tension holding plate 132 is a further grooved ballbearing 133, which interacts with a cam disk 134, which is likewisefixed to the shaft 120. A tension spring 135 connects the hold-down 103to the grooved ball bearing 133 in the tension holding plate 132.

Mounted above the elements described in FIGS. 3 through 5 is asubassembly shown in more detail in FIGS. 6 and 7. The subassemblycontains offset rollers 136, 137, which interact with the tongues 101,102. The offset rollers 136, 137 are fixed to an aluminum tube 138. Thealuminum tube 138 is guided in sliding bearings such that it can bedisplaced on a drive shaft 139. By a bushing 140 which is provided witha longitudinal slot, and with the aid of a pin that is screwed into thedrive shaft 139, the torque is transmitted to the offset rollers 136,137 by the drive shaft 139, which is driven by a stepping motor. Astepping motor 141 with attached spindle effects the lateraldisplacement of the offset rollers 136, 137 on the drive shaft 139. Theforces for the lateral displacement of the offset rollers 13.6, 137 aretransmitted by an articulated head 142, which is secured againstrotation on the spindle.

Guided in the articulated head 142 is a rod 143, which is screwed into asetting ring 144, which is not rotated at the same time. The articulatedhead 142 and the rod 143 are necessary in order to raise the offsetrollers 136, 137 off the tongues 101, 102. When the offset rollers 136,137 are being raised, the rod 143 is able to slide through thearticulated head 142 with a clearance fit. The raising action isachieved via lateral lever arms 145, 146. The lever arms 145, 146 aremounted in a holder 147 such that they can be pivoted about a shaft 148.

When the upper subassembly is put together with the lower subassembly,grooved ball bearings 149 fixed on the lever arms 145, 146 rest on camdisks 150, 151 which are fixed to the shaft 107. The upper subassemblyincludes a paper feed 152, a pair of rollers 153 being provided in thetransport path of the sheets. The rollers of the pair of rollers 153 canbe driven independently of one another by motors, by which a skewedsheet can be aligned by accelerating one of the rollers. Following thealignment of a sheet, its lateral position can be registered, forexample using a linear CCD. Using computing means, the differencebetween the center of the sheet and the theoretically accurate centralposition of the sheet can be determined, and can be corrected with theaid of the lateral displacement of the offset rollers 136, 137. Thecorrection to the deviation of the sheet centers from the center of thepaper path is carried out in a similar manner as well during theproduction of sheet stacks with sheets located so as to be offset.

The cam disks 104–106, 121–123, 134, 150, and 151 have the correspondingphase angles and geometries corresponding to the movement sequencealready described in relation to FIGS. 1.1 through 1.11 and 2. Theentire holding and depositing procedure is run through with onerevolution of the shaft of the motor 113.

In the following text, the intention is to discuss the function of theabove-described elements in more detail. The tension holding plate 132and the tension spring 135, in conjunction with the cam disk 134, havethe effect of completely relieving the tension on the hold-down 103shortly before the hold-down 103 is drawn out of the interspace betweena newly deposited sheet and the stack already formed. In this state, thehold-down 103 does not exert any holding forces on the stack. While thehold-down 103 is being relieved of tension and drawn out of the stack,the tongues 101, 102 perform the clamping of the top sheets. The sheetnewly deposited above the tongues 101, 102 is held by the offset rollers136, 137.

Before the tongues 101, 102 are drawn back out of the stack and thehold-down 103 takes over the clamping of the sheet stack, the tongues101, 102 are first raised considerably from the sheet stack by the camdisks 104, 106. It would also be possible to implement atension-relieving operation as has already been described in relation tothe hold-down 103. A few milliseconds before the tongues 101, 102 areraised, the raising of the offset rollers 136, 137 begins, brought aboutby the cam disks 150, 151. This premature raising of the offset rollers136, 137 off the tongues 101, 102 is necessary in order that the sheetconveyed out between the offset rollers 136, 137 and the tongues 101,102 is released and ultimately held only by the hold-down 103. As thetongues 101, 102 are raised, the two lateral sheet edges are raised to aslight extent at the same time. When the tongues 101, 102 are drawn awayfrom the sheet stack 1, by the cam disks 121, 122 in the next step, thenthe sheet stack 1 is released by tongues 101, 102, and the conveyedsheet is deposited on the already existing stack 1.

The cam disks 104, 106, 121, 122 are such that as the tongues 101, 102are advanced quickly over the stack, the tongues 101, 102 remain in araised position, so that they can be moved safely over the stack. Onlyshortly before the final position of the tongues 101, 102 as they areadvanced rapidly over the stack are the tongues 101, 102 lowered ontothe stack by the cam disks 104, 106. A newly conveyed sheet cansubsequently move onto the stack over the tongues 101, 102, the offsetrollers 136, 137 still being in a raised position because of the camdisks 150, 151; that is to say, there is no contact between the tongues101, 102 and the offset rollers 136, 137. Before the offset rollers 136,137 are lowered by the cam disks 150, 151, the offset rollers 136, 137are brought up to sheet advance speed. After the offset rollers 136,130.7 have been lowered, these take over the sheet transport onto thestack still before the pair of rollers 153 releases the sheet in thepaper feed 152. The correction to the skewed position of a sheet by thepair of rollers 153 is concluded before the offset rollers 136, 137 areplaced on said sheet.

In the paper feed 152, in the conveying path of the sheet and directlydownstream of the pair of rollers 153, two detectors for the sheettrailing edge can be provided spaced apart from one anotherperpendicularly in the conveying direction. As a result, the sheets canbe deposited irrespective of their format. The detector signals are usedto start the motor 113 and to correct the skewed position of the sheets.Following each deposition cycle, the deposition system finds itself in arest position, in which the hold-down 103 rests on the sheet stack, thetongues 101, 102 are in the withdrawn position and the offset rollers136, 137 are raised.

In addition to the variants described above, however, the sheet leadingedge can also be detected. For this purpose, the information relating tothe sheet length must be made available to the deposition system. Usingthis information, the appropriate time delay for the starting point ofthe deposition cycle is then determined.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it will be understood thatvariations and modifications can be effected within the spirit and scopeof the invention.

PARTS LIST

-   1 Stack-   2 Sheet-   3, 4 Roller-   5, 6 Tongue-   7 Hold-down-   8 Line-   9 Stack edge-   10 Conveying direction-   11 Mid-line-   12, 13 Side edges-   14, 15 Stepping motors-   16 Arrow-   17 Frame-   18 Direction-   19 Direction-   20 Frame-   21 Direction-   22, 23 Surface-   24 Underside-   25 Leading edge-   26 Trailing edge-   27 End-   101, 102 Tongue-   103 Hold-down-   104–106 Cam disks-   107 Shaft-   108 Frame-   109–111 Toothed-belt pulleys-   112 Toothed belt-   113 Motor-   114, 115 Rotary joint-   116 Holding plate-   117 Shaft-   118 Rotary joint-   119 Holding plate-   120 Shaft-   121–123 Cam disk-   124 Grooved ball bearing-   125–127 Sliding covering-   128–130 Tension spring-   131 Shaft-   132 Tension holding plate-   134 Cam disk-   135 Tension Spring-   136, 137 Offset roller-   138 Aluminum tube-   139 Drive shaft-   140 Bush-   141 Stepping motor-   142 Articulated head-   143 Rod-   144 Setting ring-   145, 146 Lever arms-   147 Mounting-   148 Shaft-   149 Grooved ball bearing-   150, 151 Cam disk-   152 Paper feed-   153 Pair of rollers

1. Apparatus for depositing sheets, conveyed in a conveying direction,on a stack, comprising: rotating frictional elements (3, 4), saidrotating frictional elements (3, 4) being rotatable at different speedsto accommodate for sheet skew and being movable in the verticaldirection (18) perpendicular to the conveying direction (10) of sheets(2) to be lowered onto the stack (1), a device for conveying sheets froma printing machine over the stack into the active range of said rotatingfrictional elements, on the side of the stack (1) that faces theprinting machine, tongues (5, 6) with which said rotating frictionalelements (3, 4) can be brought into and out of contact and which can bemoved in the conveying direction (10) of sheets (2) and in the oppositedirection and can be lowered onto the stack (1), and wherein on the sideof the stack (1) that faces the printing machine, at least one hold-down(7) is provided which can be moved in the conveying direction (10) ofsheets (2) and in the opposite direction and can be lowered onto thestack (1).
 2. The apparatus as claimed in claim 1, wherein said rotatingfrictional elements (3, 4) are two rollers arranged coaxially andtransversely with respect to the conveying direction (10).
 3. Theapparatus as claimed in claim 2, wherein said rollers (3, 4) can beadjusted transversely with respect to the conveying direction (10)during the conveying operation.
 4. The apparatus as claimed in claim 1,wherein the respective surfaces (22) of said tongues (5, 6) that facesaid rotating frictional elements (3, 4) respectively have asignificantly lower coefficient of friction than the surfaces (23) thatface the stack.
 5. The apparatus as claimed in claim 1, wherein said atleast one hold-down (7), acts by friction, for sheets (2), on thetrailing end of a sheet (2) that has been aligned with and deposited onthe stack (1).